Within-subjects experiments on blocking and facilitation in honeybees (Apis mellifera).

It has long been suspected in the vertebrate literature, but demonstrated only recently in work with honeybees (Apis mellifera), that the different treatments of nontarget stimuli in conventional between-groups blocking experiments may give the appearance of blocking independently of experience with the target stimulus. The same difficulty does not arise in within-subjects experiments, and in a series of such experiments with odors and colors free-flying honeybees gave no evidence of blocking; separate reinforced presentations of one element of a reinforced compound failed to reduce responding to the second. There was, however, clear evidence of facilitation; separate nonreinforced presentations of one element of a reinforced compound increased responding to the second. The implications of the results for further work on compound conditioning in honeybees and other animals are considered.

Target-absent controls in blocking experiments with rats.

In three between-groups blocking experiments with rats, two concurrent and one forward, several common control procedures were employed: Reinforced trials with the putative blocking stimulus were either omitted entirely (Kamin control), replaced by unsignaled reinforcements (Wagner control), or replaced by reinforced trials with a different stimulus (C+ control). In each experiment, parallel treatments with the target stimulus absent during training served to examine the possibility that differential responding in tests with the target stimulus might be traced solely to differential exposure to the nontarget stimuli. In Experiment 1, responding by a concurrent blocking group during the test was no different than responding by a Kamin control group, and responding by a Wagner control group was greater than that of either of the other groups--a pattern of results, mirrored in the performance of the target-absent groups, that could be attributed to the elevation of contextual excitation by unsignaled reinforcement. In Experiment 2, responding in the test by a concurrent blocking group was no different than that by a C+ control group. In Experiment 3, a finding of less responding by a forward blocking group than by a C+ control group when the target stimulus was present during training, but not when it was absent, provided plausible evidence of blocking.

Delayed symbolic matching in honeybees (Apis mellifera).

In a recent experiment on short-term memory (P. A. Couvillon, T. P. Ferreira, & M. E. Bitterman, 2003), honeybees (Apis mellifera) learned to choose between 2 colors on the basis of immediately preceding experience with 1 of them. Some learned to choose the same color as the sample (perseveration or matching), others to choose the alternative color (alternation or nonmatching). Performance in the 2 problems was very much the same. In the present experiment, honeybees learned no less readily to choose between the 2 colors on the basis of sample stimuli that were different from the colors (symbolic matching). A simple associative interpretation of the results is proposed.

Blocking and pseudoblocking: new control experiments with honeybees.

Prompted by doubts about the adequacy of the various control procedures long used in research on blocking, we repeated some earlier experiments with honeybees that had given the appearance of forward, concurrent, and backward blocking. The new experiments differed from the earlier experiments only in that the target stimulus was omitted during the training and was encountered for the first time in the test. In the new experiments, just as in the earlier experiments, the blocking groups responded less to the target stimulus than did the control groups. The results show that the effects of the different treatments of nontarget stimuli commonly compared in blocking experiments may generalize to the target stimulus and thus affect responding to that stimulus independently of experience with it. Implications for research on blocking in honeybees and other animals are considered.

The role of context in the inhibitory conditioning of honeybees.

Conditioned inhibition or CI training (A+/AB-) was compared with S- training (A+/B-) in three experiments on proboscis-extension conditioning in harnessed honeybees. The purpose was to test the Rescorla-Wagner assumption, widely credited in the vertebrate literature, that a nonreinforced stimulus acquires inhibitory properties in proportion to the excitatory value of the context in which it is presented. In prior work with free-flying honeybees pretrained with sucrose to come of their own accord to the experimental situation, no differences were found in the consequences of CI and S- training, perhaps because A added little to the excitatory value of the context (already very high) in which B occurred. In the new experiments, with harnessed subjects brought involuntarily into the training situation, negative results again were obtained. The possibility is considered that inhibitory conditioning in honeybees is independent of the excitatory value of the context.

Backward blocking in honeybees.

Three experiments with foraging honeybees were designed to study the effect of experience with A on responding to B after AB+ training. In the first experiment, responding to B was the same whether the AB+ training was preceded or followed by A+ training. In the second experiment, responding to B after AB+ training was less in animals that also had A+ training than in control animals that were equally often reinforced in the absence of A; whether the A+ training preceded, was concurrent with, or followed the AB+ training made no difference. In the third experiment, responding to B after AB+ training was less when the AB+ training was followed by A+C- training than when it was followed by C+/A- training. These results, like those of some recent vertebrate experiments, take us beyond the traditional explanation of blocking in terms of impaired conditioning of B on AB+ trials and support the suggestion that the mechanism, still poorly understood, may nevertheless be a relatively simple one.

Inhibitory conditioning in honeybees.

Honeybees were rewarded with sucrose solution for choosing AX(a grey target, X, labelled with a distinctive stimulus, A) rather than ABX (a grey target labelled both with A and with another distinctive stimulus, B)-AX+/ABX- training. Tests of independent groups made after such training showed a clear preference not only for AX over ABX, but also for ABX over BX, and for X over BX. These experiments, along with some earlier ones to which they bring a new perspective, provide persuasive evidence, previously lacking, of inhibitory conditioning in honeybees.

Delayed alternation in honeybees (Apis mellifera).

Previous experiments with honeybees (Apis mellifera) failed to show learned control of performance by short-ten memory. In this study, honeybees were trained with an improved technique to choose 1 of 2 colors that was either the same as a recently rewarded sample (perseveration) or different (alteration). Because any increase in associative strength stemming from the sample experience would tend to promote perseveration and contravene alternation, the equal difficulty of the 2 tasks suggests that the role played by the sample was primarily discriminative. The animals remembered on each trial the immediately preceding experience with reward and learned to use that information appropriately. These new results extend the list of what may well be fundamental similarities in the learning of vertebrates and honeybees.

The role of nonreinforcement in the learning of honeybees.

Two series of experiments with honeybees were designed to test the assumption that inhibition is generated by nonreinforcement as a function of the excitatory value of the context. In the first series (Experiments 1-3), summation tests with B were made after A+/C-/AB- as compared to A+/C-/CB- training, with precautions taken to minimize the possibility of a masking effect of excitatory within-compound conditioning on AB trials; responding to B did not vary with training procedure. In the second series (Experiments 4-5), retardation tests rather than summation tests were used, in the belief that they might be more sensitive; after A+/AB-/CD- training, acquisition in a B+/D- problem was found to be no less rapid than in a D+/B- problem. A third series of experiments (Experiments 6-9) was designed to test the more general assumption that the effectiveness of nonreinforcement increases with the excitatory value of the context; response to B was found to be no different after A+/B+/C- training followed by A+/AB- training than after A+/B+/C- training followed by A+/CB- training. The results are compatible with the view that the role of nonreinforcement in honeybees is not to generate inhibition, but only to reduce excitation in a manner independent of the excitatory value of the context.

Quantitative tests of an associative theory of risk-sensitivity in honeybees.

Risk-sensitivity was studied in free-flying honeybees trained individually to choose between two scented targets (A and B) with varying amounts and concentrations of sucrose solution as reward. In the first phase of experiment 1, the animals showed "risk-aversion," preferring A, which provided 5 microl of a 40 % sucrose solution on every trial, to B, which provided 30 microl of the same solution once in every six trials (mean amount per trial 5 microl for each alternative). In the second phase, the preference reversed with reversal of the reward assignments. In experiment 2, the consistently rewarded A (5 microl of 40 % sucrose solution per trial) was again preferred, although the inconsistently rewarded B now provided twice the amount of sucrose solution on average (30 microl on two of every six trials, mean amount per trial 10 microl). In experiment 3, with A providing 10 microl of a 15 % sucrose solution on every trial and B providing 10 microl of a 60 % sucrose solution on two of every four trials (mean concentration per trial 30 %), the animals preferred B. In Experiment 4, patterned after experiment 1, similar results were obtained under more natural conditions in which the animals were no longer constrained (as they were in the first three experiments) to go equally often to each alternative. The results of all four experiments were predicted quantitatively and with considerable accuracy by a simple associative theory of discriminative learning in honeybees.

Intermodal blocking in honeybees.

Previous findings of intramodal but not of intermodal blocking in foraging honeybees prompted a new series of experiments with colours, odours, a proximal visual landmark, and a localized geomagnetic anomaly as stimuli. In Experiments 1-2, the landmark was blocked by both colour and odour. In Experiments 3-6, the anomaly was blocked by both colour and odour, but the anomaly failed to block either colour or odour. In Experiments 7-8, the anomaly failed again to block either colour or odour even though it could be shown to develop substantial associative strength in the course of the training. The several instances of intermodal blocking bring the results for honeybees into closer agreement than before with the results for vertebrates. The failures of blocking seem understandable in terms of the relative salience of the stimuli employed without reference to modal relationships. An attentional interpretation is suggested.

Exploratory studies of inhibitory conditioning in honeybees (Apis mellifera).

The best available evidence of inhibitory conditioning in vertebrates comes from experiments in which variants of A+/AB- and A+/B- training were compared in terms of response to B in summation and retardation tests, the results suggesting that inhibition is generated by nonreinforcement as an increasing function of the excitatory value of the setting. We report here 7 experiments with foraging honeybees (Apis mellifera) that failed to show a difference in the effects of the 2 treatments. On the basis of previous experiments as well as supplementary experiments whose results give no reason to doubt the sensitivity of the training techniques and measures used, our consistently negative results may mean either that inhibition in honeybees is generated by nonreinforcement independently of the setting or that there is no inhibitory conditioning at all in honeybees--that the only associative function of nonreinforcement is to reduce excitatory strength.

Quantitative two-process analysis of avoidance conditioning in goldfish.

The shuttlebox performance of goldfish was studied under standardized conditions in a variety of problems--with or without an avoidance contingency, a conditioned stimulus (CS)-termination contingency, and an escape contingency. The effects of CS-only, unconditioned stimulus (US)-only, and explicitly unpaired training were also examined. All the data could be simulated quantitatively with a version of O. H. Mowrer's (1947) 2-process theory expressed in 2 learning equations (1 classical, the other instrumental) and a performance equation. The good fit suggests that the theory is worth developing further with new experiments designed to challenge it.

Amsel's analysis of reward-schedule effects.

Some questions raised by Amsel's valuable review of his extensive research on reward-schedule effects are considered-questions about the nature of instrumental conditioning, about the distinction between long- and short-term memory, and about evolutionary divergence in learning.

The two-test strategy in the study of inhibitory conditioning.

It is commonly believed that both a summation test and a retardation test should be used to determine whether a stimulus becomes inhibitory in consequence of some specified treatment, because the 2 tests together rule out alternative interpretations. Depending, however, on the choice of control treatments, a single test may provide credible evidence of inhibition or both together may not. A comprehensive review of the 2-test literature shows that suitable controls have been used only rarely and that compelling evidence of inhibition is correspondingly rare. The only such evidence now available is provided by retardation tests in experiments with some variation of A+/AB- training as the putatively inhibitory treatment.

Simultaneous conditioning in honeybees (Apis mellifera).

Honeybees (Apis mellifera) were classically conditioned with odor as conditioned stimulus (CS), sucrose as unconditioned stimulus (US), and proboscis extension as response. The purpose of Experiment 1 (Ns = 26 and 27) was to look for facilitation of forward conditioning by CS-US overlap, but rapid conditioning without overlap left little room for improvement. In 2 further experiments, CS and US were simultaneous, and response to odor alone was measured in subsequent tests. In Experiment 2, a Simultaneous group (N = 25) responded more to the training odor than did an Unpaired control group (N = 25). In Experiment 3, a differentially conditioned Simultaneous group (N = 29) responded more to an odor paired with sucrose in training (S+) than to an odor presented alone (S-). The implications of the results for the problem of the role of amount of reward in honeybee learning are considered.

Learning in honeybees (Apis mellifera) as a function of sucrose concentration.

Foraging honeybees (Apis mellifera) were trained with 2 successively presented targets differing in color or odor, one of which always contained a 5-microliters drop of 50% sucrose solution and the other, a 5-microliters drop of 20% sucrose solution. Latency of response to each target was measured during the training, and at the conclusion, preference was measured in an unrewarded choice test. Analysis of the latencies showed both a prospective effect (faster response to the 50% target than to the 20% target) and a nonassociative retrospective effect (faster response after leaving the 20% target than after leaving the 50% target) reminiscent of the frustration effect in rats. The results both for prospective latency and for choice can be understood on the simple theory that the attractiveness of a target depends on the strength of its association with sucrose and that the effect of concentration is on asymptotic strength.

Appetitive conditioning in Octopus cyanea.

The performance of Octopus cyanea was studied in 3 appetitive conditioning situations. In Experiment 1, 2 groups were trained in a runway; a large reward produced faster acquisition when reinforcement was consistent and better subsequent performance on a partial schedule than did a small reward. In Experiment 2, activity in the vicinity of a feeder was measured, and in Experiment 3, latency and probability of response were measured in an automated version of a traditional conditioned attack situation (Boycott & Young, 1950). There was evidence of acquisition with continuous reinforcement in both experiments but in neither with partial reinforcement. All of the results can be understood in terms of growth and decline in the strength of stimulus-reinforcer associations with reinforcement and nonreinforcement.